Error in writing to directory /tmp/OraInstall2007

I successfully start a VNC session on our Unix box. Then I run the
installer, and it returns the message below. There is about 800MB free
space in /tmp and I have confirmed the /tmp directory is writable by
user oracle. This used to work. My colleague upgraded from 10.2.0.2 to
10.2.0.3 recently, and I wonder if this is part of the reason we now
encounter this problem. Our OS is AIX 5.3. Running the installer does
create directory OraInstall2007-10-10_10-38-29AM. This directory
contains an installActions log file and also a sub-directory named jre.
Jre contains a directory lib, which contains a bunch of files (mostly
font.properties).

Can anybody provide advice on what the problem may be? This is what I
get when I run the installer from /tmp:

$ /u01/app/oracle/product/10.2/oui/bin/runInstaller -debug

Starting Oracle Universal Installer...

No pre-requisite checks found in oraparam.ini, no system pre-requisite
checks will be executed.